1. Field of Invention
The present invention relates to a signal generating and switching apparatus in an integrated circuit and a method thereof. More particularly, the present invention relates to a signal generating and switching apparatus in an integrated circuit capable of changing a metal layer many times and a method thereof.
2. Description of Related Art
Generally speaking, common electronic circuits require a circuit capable of providing signals of a specific logic value, for example, the circuit for recording version information in an integrated circuit. FIG. 1 is a principle diagram of a signal generating apparatus 100 in a metal layer of an integrated circuit according to the prior art. FIG. 1 shows a signal generating apparatus for one bit of the version information as an example to illustrate the signal switching principle of the prior art. As shown in FIG. 1, the signal generating apparatus 100 of the prior art comprises a switch 102 and a switch 104.
The integrated circuit comprises a plurality of conductive layers including metal layers and polysilicon layers. In the conventional layout technique for the integrated circuit, a top metal layer is usually used to record the version information of the integrated circuit. That is, the switches 102 and 104 of the signal generating apparatus 100 are disposed on the top metal layer. A logic high level “1” is input from the first end of the switch 102 and the logic low level “0” is input from the first end of the switch 104. When the bit information is changed, the switches 102 and 104 can be turned on or off to output a specific logic signal.
Therefore, if there is a need to change the circuit of one of the plurality of conductive layers in the integrated circuit, although the change of the circuit on the top metal layer is not desired, the top metal layer will still be changed at the same time in order to update the version information. In other words, not only the mask for the internal conductive layer of a circuit is to be changed, but also the mask for the top metal layer must be re-fabricated, so as to update the version information, thus significantly increasing the correcting cost of the integrated circuit.